As an Academic Research Enhancement Award project, this project aims at enhancing biomedical and behavioral research conducted at an institution of higher education that has not been a major recipient of NIH support in the past. Research funds will support the principal investigator's continuing research activities, will strengthen the institution's research environment, and will provide undergraduate students with the benefit from exposure to and participation in research. The research project will investigate a sensory mechanism ("dark adaptation") of great importance for the understanding of the process by which circadian rhythms are synchronized by the daily cycle of light and darkness ("entrainment"). The specific aims are to investigate whether several mammalian species exhibit the process of circadian dark adaptation recently demonstrated in golden hamsters and mice, to evaluate whether circadian dark adaptation is a sensory process similar to that well established in the visual system, and to determine whether circadian dark adaptation occurs peripherally or centrally. The knowledge that will be gained through this project will advance the current understanding of the mechanism of entrainment. Entrainment is a process of utmost importance for animals and humans living under natural conditions, where the timing of behavioral and physiological processes must be coordinated with the daily alternation of day and night. A better understanding of entrainment has potential applications in the prevention of jet lag and the malaise associated with shift work, the treatment of sleep disorders and depression, the scheduling of optimal times for administration of medicines, and the planning of astronaut schedules for space exploration.